While adhering the back on one of my builds I feared a sloppy join at the heel block. In my wisest of moves I applied a nice shot of gorilla to the heelbock feeling confident that it would expand a little and fill the gaps, trying to avoid the dreaded back dimple. When I removed the guitar from the solara the next day I was horrified to find that it had squeezed out and foamed all over like that bridge in the picture. It didn't just foam out, it dripped in thick strings, like an extra-hot grilled cheese sandwich held in midair. Stuff was everywhere. Cutting it out cleanly through the sound hole was ridiculously hard. I managed to ding up the edge of the sound hole while trying to cut it out. So I then tried to sand out the dings in the sound hole rim and made it uneven and silly looking. The area of glue that I was able to cut away looked butchered......and I still got a nasty dimple on the back. I then proceeded to teach myself that you cannot sand a dimple flat with 80 grit paper to improve its appearance.

Fixing errors with glue and sandpaper requires a stonger skill set than the botched task that created the need to fix it in the first place.

Whenever I see those orange labeled bottles at the hardware store I find myself filled with a little bit of misplaced hatred towards gorillas.

Great story Brian! Gorilla glue foam is the nastiest stuff on earth. I could not imagine looking in the sound hole and seeing what looks like a rabid dog staring back at you.

The only thing I use Gorilla glue on is when making binding + purfling sandwiches before bending. Gorilla glue does not let go under heat, so you never have to worry about the purfling delaminating from the binding when bending.

Gorilla glue has a great reputation for gap filling, but some strength tests whose references fail me (but either Fine Woodworking or Popular Woodworking) suggested that the filled gaps had no inherent strength to them. I recall that conventional glues actually ended up giving stronger bonds in poorly fitted joints. I hope I'm not spreading alternative facts here.

Jim yes I saw that article - Fine Woodworking I think some time back. The strong conclusion was that none of our commonly used woodworking glues are gap fillers, including the stuff in the yellow bottles. The only gap filler is reckoned to be epoxy, possibly with a filler to stop it running out of any spaces.

Chessmonkey wrote:Hi,
I realize this thread is a year old but I was hoping I could jump in and get a question answered. Is this foaming the result of Gorilla Glue and can I trim it off with a sharp blade? Here's a picture:

Please please clarify what's happening here. Is this yours? Did you glue a bridge with the strings still attached?

To answer your actual question, yes that is the normal foaming result of Gorilla Glue's normal curing/drying process.

Brian McCombs wrote:While adhering the back on one of my builds I feared a sloppy join at the heel block. In my wisest of moves I applied a nice shot of gorilla to the heelbock feeling confident that it would expand a little and fill the gaps, trying to avoid the dreaded back dimple. When I removed the guitar from the solara the next day I was horrified to find that it had squeezed out and foamed all over like that bridge in the picture. It didn't just foam out, it dripped in thick strings, like an extra-hot grilled cheese sandwich held in midair. Stuff was everywhere. Cutting it out cleanly through the sound hole was ridiculously hard. I managed to ding up the edge of the sound hole while trying to cut it out. So I then tried to sand out the dings in the sound hole rim and made it uneven and silly looking. The area of glue that I was able to cut away looked butchered......and I still got a nasty dimple on the back. I then proceeded to teach myself that you cannot sand a dimple flat with 80 grit paper to improve its appearance.

Fixing errors with glue and sandpaper requires a stonger skill set than the botched task that created the need to fix it in the first place.

Whenever I see those orange labeled bottles at the hardware store I find myself filled with a little bit of misplaced hatred towards gorillas.

It's not affected by heat? I couldn't use, say, a heated knife blade to slice off the extrusion along the join?

MessyTendon wrote:Sounds good, hopefully the client will be happy too. One more possibility, you might need a solvent to break the bond. If you knew what it was that would be a lot easier. But a solvent should break it down. I would try the solvent, then you could open the back but avoid a re-top. With small drops in a pipette or small syringe you could put little drops on and see what happens, a sharp thin knife to break the bond.

I just hate seeing a good top go to waste. But if it's necessary that's just the way the cookie crumbles.